Method of producing a laminated packaging material

ABSTRACT

The invention relates to a method of producing a laminated packaging material ( 10 ) including a core layer ( 16 ) of paper or paperboard and a barrier layer ( 14 ) applied on one side of the core layer. The invention also relates to a laminated packaging material ( 10 ) produced according to the method, as well as a packaging container ( 50 ) which is produced from the laminated packaging material ( 10 ).

FIELD OF THE INVENTION

The present invention relates to a method of producing a laminatedpackaging material comprising a core layer of paper or paperboard and abarrier layer applied on one side of the core layer.

The present invention also relates to a laminated packaging materialproduced according to the method, as well as to packaging containerswhich are produced from the laminated packaging material. Particularlyadvantageous packaging laminates in which polyvinyl alcohol or starch incombination with nanoparticles is used as a barrier layer material areprovided.

BACKGROUND OF THE INVENTION

It is well-known in the packaging industry to employ laminated packagingmaterial of a single-use nature for packing and transporting liquidfoods. Normally, such laminated packaging materials are built up from aconfigurationally rigid but foldable core layer consisting of, forexample, paper or paperboard in order to achieve good mechanicalconfigurational stability. Liquid-tight coatings of plastic are appliedon both sides of the core layer and effectively protect the core layerof liquid-absorbing fibre from penetration by moisture. These outerlayers normally consist of a thermoplastic, preferably polyethylene,which moreover impart to the packaging material superior thermosealingproperties, whereby the packaging material may be converted intofinished packages with the desired geometric configuration.

However, laminated packaging material consisting solely of paper orpaperboard and liquid-tight plastic lacks tightness properties vis-a-visgases, in particular oxygen gas. This is a major drawback in the packingof many foods whose shelf-life deteriorates dramatically when in contactwith oxygen gas, such as for example fruitjuices. In order to supplementthe packaging material with a barrier against gases, especially oxygengas, it is known in the art to apply a layer possessing superior oxygengas tightness properties, for example aluminum foil or polyvinylalcohol, on that side of the core layer which is intended to face intowards the inside of the package.

In comparison with aluminum foil, polyvinyl alcohol enjoys manydesirable properties, with the result that it is preferred as barriermaterial in many contexts. Among these, mention might be made of thepolyvinyl alcohol's superior strength properties, compatibility withfoods and economic value, together with its excellent oxygen gas barrierproperties. Moreover, it has been considered to be expedient, in certaincases from the point of view the environment and recycling, to replacealuminum foil as the gas barrier material in food packages.

Like many other conceivable barrier or adhesive polymers such as, forexample, ethylene vinyl alcohol, starch, starch derivate, carboxy methylcellulose and other cellulose derivates or mixtures thereof, polyvinylalcohol is suitably applied by means of a coating process, i.e. in theform of a dispersion or aqueous solution which, On application, isspread out to a thin, uniform layer on the substrate and thereafterdried. We have found that one drawback in this process however is thatan aqueous polymer dispersion or polymer solution of, for example,polyvinyl alcohol with an addition of EAA which is applied on a corelayer of paper or paperboard penetrates into the liquid-absorbing fibresof the core layer. In connection with the removal of water for dryingand possibly for curing the applied barrier layer, the core layer isalso subjected to elevated temperatures for drying, and as a result therisk of undesirable crack formation in the paperboard or paper layer,respectively, increases as a result of the moisture content which isdifficult to adjust, and the drying which takes place in this layer.

Swedish Patent No. 440519 proposed including a thickening agent such asalginate to reduce penetration of water into the board. The use of PVOHas a barrier material applied over a polymer layer preventing crackformation and smoothing the board surface was disclosed in WO97/13639.

One drawback is that the polyvinyl alcohol is moisture sensitive andrapidly loses its barrier properties when it is exposed to a dampenvironment. This inconvenience was previously obviated according toWO97/22536 by combining the polyvinyl alcohol with one or more per seknown food-approved polymers, for example ethylene acrylic acidCopolymer (EAA) or styrene butadiene copolymer. These advantageouslyform, in combination with polyvinyl alcohol, a coherent, well integratedlayer possessing superior gas barrier properties, in particular oxygengas barrier properties, at the same time as the desired superior gasbarrier properties of the polyvinyl alcohol are retained even in a dampenvironment.

WO97/22536 disclosed that polyvinyl alcohol mixed with EAA-ethylenecopolymer or the like material could be dispersion coated onto apaperboard previously coated with a polymer and thereafter could bedried and cured at temperatures of up to 170° C. to form a laminatedpackaging material with a very good barrier property.

Without being restricted to any particular theory, it is suggested thatthe improved oxygen and water barrier properties results from anesterification reaction between the PVOH and the EAA all the increasedcuring temperature, whereby the PVOH is crosslinked by hydrophobic EAApolymer chains, which thereby are built into the structure of the PVOH.

Another drawback in the employment of, for example, polyvinyl alcohol asbarrier layer instead of aluminum foil is that, on storage oflightsensitive foods, it is necessary in many cases also to incorporateinto the packaging material a light barrier of some type. Granted, acore layer of paper or paperboard does not (to the naked eye) allow thepassage of any light, but light in invisible wavelength rangesnevertheless penetrates through from the outside of a packagingcontainer to the packed food product and may have a negative effect onit from the point of view of shelflife. The employment of aluminum foilin the packaging material enjoys that advantage that the aluminum foilin itself constitutes a good barrier against both gases and againstlight. On the other hand, polyvinyl alcohol is as good as completelytransparent even in mixtures with a hydrophobic polymer such as ethyleneacrylic acid copolymer or styrene butadiene copolymer. The admixture ofconventional light barriers, such as carbon black and titanium dioxideinto any of the plastic layers included in the laminated packagingmaterial according to WO97/22536 is per se possible, but would entail anaesthetically unattractive appearance in the package.

Yet a further drawback inherent in the laminated packaging materialincluding barrier layers of, for example, polyvinyl alcohol possiblytogether with another polymer is that this packaging material cannot beproduced employing the same production equipment as in the production ofpackaging material using aluminum foil as the barrier layer, whichinvolves capital investment costs for new production equipment.

As indicated above, PVOH has environmental benefits as a barriermaterial. In addition to such synthetic materials, the possibility ofusing natural and biodegradable polymers (biopolymers) such as starchand starch derivatives, as gas barrier materials has been investigated.

It is previously known that starch possesses some gas barrier propertieswhen employed in relatively thick layers, such as in films having athickness of about 20 to 30 μm. Such thick layers of starch material arenot suitable for use in packaging laminates however, since they becomebrittle and are prone to cracking and breaking upon handling, forexample in the lamination process and when fold forming of the laminateinto packages. Besides not being flexible in handling at manufacturingand distribution, laminates including such thick layers of starch mayalso absorb moisture and cause delamination between the starch layer andits adjacent layers.

From WO97/16312 it is known that very thin layers of starch applied onto a core layer may provide some gas barrier properties, at least whenemployed together with an adjacent layer of plastics, which has beenunited with starch barrier layer by extrusion coating of the plasticsmaterial. Two very thin layers of starch, applied in a quantity of 0.5and 1 g/m² respectively, dry weight, on to opposite sides of a corelayer of paperboard and each extrusion coated with a layer of plastics,provided an oxygen gas barrier of 289 cm³/m², per 24 h at 1 atm.Similarly, two layers of starch, applied in a quantity of 1 and 1.5 g/m²respectively, provided an oxygen gas barrier of 141 cm³/m², per 24 h at1 atm. The results obtained were thus, comparable with the gas barrierproperties of, for example, a 12 μm thick film of oriented PET, thusrepresenting a ‘medium performance barrier’ material.

The packaging laminate WO97/16312 is, however, merely a mediumperformance gas barrier material. This means that it may only be usedfor packaging of liquid food products during short time periods of coolstorage. It is not hitherto known in the prior art to produce packaginglaminates having high performance gas barrier properties from starch ofor starch derivative barrier materials. It would be much more desirableto be able to provide packaging material having sufficient gas barrierproperties for long time storage of liquid food products, i.e. forextended shelf life (ESL) at cool storage or even for aseptic storage.Such desirable high performance oxygen gas barrier properties are in theorder of about 50 cm³/m² at 24 h, 1 atm (23° C., 50% RH) or better, e.g.up to 30 cm³(m² at 24 h. 1 atm, i.e. oxygen gas barrier propertiescomparable to those of, for example, PVOH, EVOH (ethylene vinyl alcoholcopolymer) or polyamides (PA) when employed at a thickness of the orderof about 5 μm.

FR-A-2684922 discloses coating a polymer film such as polyester with adispersion of amylose starch containing surfactant and drying the starchat a temperature of up to 180° C. Good gas barrier properties areobtained at coating levels of for instance 0.7 g(dry)/m². However, thereis no indication that similar properties might be obtainable in alaminated packaging material having a paper or paperboard core.

However, although the above gas barrier polymer materials are capable ofproviding good gas barrier properties in a packaging laminate they arestill oxygen-permeable to some degree, while a metal or glass materialto be used in canning or bottling has an oxygen permeability ofsubstantially zero. In order to improve the gas barrier properties stillfurther, the polymer gas barrier material may be mixed with an inorganiclaminar compound. Such a gas barrier resin composition is for exampledescribed in EP-A-590263, wherein excellent high level gas and moisturebarrier properties are obtained. EP-A-590263 discloses a process forproducing a gas barrier resin composition or its moulded articleincluding a film, the composition comprising a resin and an inorganiclaminar compound having a particle size of 5 having a particle size of 5m or less and an aspect ratio of 50 to 5000, the process comprisingdispersing the inorganic laminar compound in a resin or resin solutionin the state that the inorganic laminar compound is swollen or clovenwith a solvent/dispersant and removing the solvent from the dispersion,if necessary in the form of a film, while keeping the laminar compoundin the swollen state.

SUMMARY OF THE INVENTION

We have now found that a laminated packaging material possessingexcellent to barrier properties, in particular against gases, may beproduced using a method which lends itself to being carried out usingconventional production equipment of the type employed in the productionof packaging materials with aluminum foil as the barrier layer.

We have also now established that it is possible in a paperboardpackaging laminate for liquid food packaging to obtain excellent highperformance oxygen barrier properties from the use of a gas barriercomposition comprising a dispersible or soluble polymer and an inorganiclaminar compound.

Furthermore, by avoiding coating the liquid gas barrier composition ontothe core layer in connection with the lamination of the packagingmaterial, we have eliminated the risk of excessive water absorption intothe core layer and consequential crack formation when drying the coatedcore layer of paper or paperboard.

According to a first aspect of the invention, there is now provided amethod of producing a laminated packaging material comprising a corelayer of paper or paperboard and a barrier layer applied on one side ofthe core layer, characterised in that a liquid gas barrier resincomposition including a dispersion or solution of a polymer and aninorganic laminar compound is applied as a barrier layer on at least oneside of a carrier layer and is dried during heating for driving off thedispersant or solvent, whereafter the carrier layer with the applied,dried barrier layer is combined and permanently united with one side ofthe core layer.

Preferably, the inorganic laminar compound or so-called nanoparticlecompound is dispersed to an exfoliated state, i.e. the lamellae of thelayered inorganic compound are separated from each other by means of aliquid medium. Thus the layered compound preferably may be swollen orcloven by the polymer dispersion or solution, which at dispersion haspenetrated the layered structure of the inorganic material. It may alsobe swollen by a solvent before added to the polymer solution or polymerdispersion. Thus, the inorganic laminar compound is dispersed to adelaminated state in the liquid gas barrier composition and in the driedbarrier layer.

The term clay minerals includes minerals of the kaolinite, antigorite,smectite, vermiculite or mica type, respectively. Specifically,laponite, kaolinite, dickite, nacrite, halloysite, antigorite,chrysotile, pyrophyllite, montmorillonite, hectorite, sodiumtetrasilicic mica, sodium taeniolite, commonmica, margarite,vermiculite, phlogopite, xanthophyllite and the like may be mentioned assuitable clay minerals.

The inorganic laminar compound or clay mineral preferably has an aspectratio of 50-5000 and a particle size of up to about 5 μm in theexfoliated state.

Preferably, the barrier layer is applied by means of liquid film coatingwith an aqueous composition of a dispersion or solution of a barrierpolymer further including the inorganic laminar compound. For examplePVOH, or PVOH and EAA, may be applied in the state of an aqueoussolution in mixture with an inorganic laminar compound, whilst starchmay be applied in an aqueous partially dispersed and/or dissolved statein mixture with the inorganic laminar compound.

Preferably, the barrier layer includes from about 1 to about 40 weight%, more preferably from about 1 to about 30. weight % and mostpreferably from about 5 to about 20 weight %, of the inorganic laminarcompound based on dry coating weight. If the amount is too low, the gasbarrier properties of the coated and dried barrier layer will not bemarkedly improved compared to when no inorganic laminar compound isused. If the amount is too high, the liquid composition will become moredifficult to apply as a coating and more difficult to handle in storagetanks and conduits of the applicator system.

Preferably, the barrier layer includes from about 99 to about 60 weight%, more preferably from about 99 to about 70 weight % and mostpreferably from about 95 to about 80 weight % of the polymer based onthe dry coating weight.

An additive, such as a dispersion stabiliser or the like, may beincluded in the gas barrier composition, preferably in an amount of notmore than about 1 weight % based on the dry coating.

The barrier layer is preferably applied on the carrier layer in anamount, depending on the kind of polymer, of approximately 0.5 to 20g/m², more preferably approximately 1-10 g/m², based on dry weight. Ifthe coated amount is too low, the gas barrier properties may beinferior, while if the amount is too high, there is a risk for aninflexible barrier layer and crack formation therein.

The polymer preferably is a high hydrogen-bonding polymer havinghydrogen-bonding groups or ionic groups to an extent of 20 weight % andabove of the polymer molecule. More preferably, the polymer hasfunctional hydroxyl groups and may for instance be selected from amongpolyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), polysaccharidessuch as starch, starch derivatives, carboxyl methyl cellulose and othercellulose derivatives, or a mixture of two or more thereof. Alsopolymers having nitrogen-containing groups may be employed. Mostpreferably, the polymer is a polymer having gas barrier propertiesitself, specifically polyvinyl alcohol, starch or a starch derivative.

Said aqueous polymer dispersion or polymer solution applied as barrierlayer may be dried and optionally cured at a web surface temperature ofapproximately 80 to 200° C. For non-curing materials it is preferred tooperate at a temperature of approximately 80 to 1300° C.

Most preferably, materials including PVOH and inorganic laminar compoundare preferably first dried at web temperatures from 80 to 160° C.(preferably 140 to 1600° C.) in a first step and are cured at webtemperatures from 170 to 230° C. in a second stage resulting in animproved gas barrier at 80% RH. Optionally, the carrier and barriermaterial may be cooled between the two steps.

A polymer with functional carboxylic acid groups may also be included.This may react with the polymer with functional hydroxy groups duringthe drying/curing process.

Suitably, the polymer with functional carboxylic acid groups is selectedfrom among ethylene acrylic copolymer and ethylene methacrylic acidcopolymers or mixtures thereof.

One particularly preferred barrier layer mixture is of polyvinylalcohol, ethylene acrylic acid copolymer (EAA) and an inorganic laminarcompound. The EAA copolymer is preferably included in the barrier layerin an amount of about 1-20 weight %, based on dry coating weight.

Another particularly preferred barrier layer mixture is of starch orstarch derivative and an inorganic laminar compound.

Optionally, the barrier layer is first dried and is then heated to ahigher temperature so that the dried barrier layer is cured at atemperature of up to 230° C. preferably approximately about 170° C. Thehigh temperature curing may be of short duration, such as correspondingto web speeds normally used in the packaging laminate production.

The carrier layer may consist of paper or plastics or plastics coatedpaper and preferred materials are described below. When paper isemployed it is preferably thin. In one option the carrier layerpreferably consists of paper with a grammage of approximately 5-35 c/m²,e.g. 7-25 g/m², more preferably approx. 10-20 g/m².

The carrier layer bearing the barrier material and the core layer may beassembled together in various ways.

The carrier layer bearing at least one said barrier layer may becombined and united with the core layer by extrusion of a layer ofthermoplastics therebetween.

Where said carrier layer bears a said barrier layer on one side thereofit therefore may be combined with the core layer by extrusion of a layerof thermoplastics between the carrier layer and the core layer.

An outer layer of thermoplastics, preferably polyethylene, is thenapplied on the barrier layer by means of extrusion.

When the carrier layer bears a said barrier layer on one or both sidesit may be combined with the core layer by extrusion of a layer ofthermoplastics between the core layer and a said barrier layer.

If said carrier layer bears a said barrier layer on both sides thereof,a layer of thermoplastics may then be applied to the outer layer ofbarrier material by extrusion.

The layer of plastics applied between the core layer and the carrierlayer or a said barrier layer may include a substance functioning aslight barrier. This is especially preferred when the carrier layer is ofpaper or other visually non-transparent material.

We have also established that it is possible in a packaging laminate toobtain high performance oxygen barrier properties from the use of a gasbarrier composition comprising a dispersion of starch and similarmaterials and an inorganic laminar compound.

A gas barrier layer including starch and inorganic laminar compound ispreferably applied at a dry coating weight of from 0.5 to 5 g/m², morepreferably 0.5 to 3 g/m² e.g. from 1.5 to 2 g/m².

It is acceptable to include minor amounts of other polymeric materialswhich do not interfere with the desired properties of the composition ofstarch and inorganic laminar compound. For instance the gas barrierlayer may further comprise a minor amount of water soluble or waterdispersible polymers having functional hydroxyl groups, e.g. polyvinylalcohol, and carboxyl group containing polyolefins such as ethyleneacrylic acid, or a mixture thereof. The amount of such materials may befrom 0 to 30%, e.g. 0 to 20% or 0 to 10% by weight.

Preferably, packaging laminates including starch in the barrier layercomprises a layer of plastics polymer, preferably a thermoplastics, e.g.polyethylene, laminated directly with the said gas barrier layer. Mostpreferably, said polymer is LDPE. Other thermoplastics that may beemployed include all other kinds of polyethylene (including LLDPE,ULDPE, VLDPE, M-PE and HDPE), polyproplylene, andpolyethyleneterephthalate.

We have observed that when polyethylene is applied to a layer based onstarch at a high temperature, e.g. over 200° C., the gas barrierproperties are improved and that under appropriate conditions can bemade to reach or move further into a high performance level. Accordingto the invention, the preferred method of obtaining optimal propertiesis to apply the barrier composition based on starch or starch derivativenot to a thick core layer as in WO97/16312 but to a separate carrier.Suitably then, the gas barrier layer is carried by a carrier layer ofpaper or plastics.

When paper is employed it is preferably thin, e.g. said carrier layermay be of paper having a surface weight of from 5 to 35 g/m², preferablyfrom 10 to 25 g/m². The paper may also be coated beforehand with a layerof plastics.

After application of the liquid composition of starch and inorganiclaminar compound, the carrier may be combined with a thicker corematerial so that the packaging laminate comprises a core layer havingsaid carrier layer on one surface side thereof. There may be one or morelayers including a heat sealing layer on the other surface side of saidcore layer.

The surface of the carrier layer to which the starch or starchderivative composition is applied is preferably substantially imperviousto said liquid vehicle.

The degree to which the surface is impervious may be measured bymeasuring surface adsorption, e.g. in Cobb units. (“Cobb”=g(water)/m²adsorbed on to the surface in 60 seconds exposure to liquid water).Adsorption of other liquids could be measured in an analogous method.The method of measuring Cobb adsorption is defined in SCAN P12-64 and inTAPPI T441. The surface adsorption of plastics is generally about 1Cobb, whilst a smooth paper surface will generally have an adsorption ofabout 20 to 30 Cobb. Suitably, for use in the invention the substratesurface should have an adsorption of 50 Cobb or less, preferably anadsorption of 30 Cobb or less, more preferably an adsorption of lessthan 20 Cobb or most preferably an adsorption of 10 Cobb or less, e.g.less than 5 Cobb.

Preferably, the surface of the carrier layer to which the composition ofpolymer and inorganic laminar compound is applied has a smoothness of200 Bendtsen or better. The method of measuring Bendtsen smoothness isdefined in SCAN (Scandinavian Pulp and Paper Norms) P21-67 and in TAPPIUM535.

Where the substrate is plastics or has a plastics surface, such desiredsmoothness is usually obtained, such as in, for example, a film ofplastics or a plastics coated paper carrier layer.

One reason why a high performance barrier property was not achieved inWO97/16312 may be that the paperboard core layer lacked the requisitedegree of impermeability so that the aqueous solution of starch whichwas employed may have penetrated the surface. This might have an adverseaction in a number of ways. There may not then be a smooth and unbrokensurface to the starch layer because of penetration as such into thepaperboard. Alternatively, or additionally, drying of the paperboard todry the starch layer may cause surface deformation of the paperboard andhence cracking of the starch layer. These problems are obviated when thestarch is applied to a separate, smooth, impervious carrier layer whichis subsequently laminated to the core layer.

The paperboard used in WO97/16312 would typically be expected to havehad a surface smoothness of 500-600 Bendtsen. This may in itself havebeen sufficient to prevent the starch layer being smooth and unbroken orfrom having thin areas providing a path for oxygen transmission.

In order to avoid cracks, punctures or deformations in the barriercomposition layer of starch or starch derivative layer and inorganiclaminar compound, it is preferred that the surface on to which it isapplied is smooth, e.g. that the substrate surface has a smoothness of200 Bendtsen or better (i.e. less), e.g. from up to 150 Bendtsen, mostpreferably up to about 100 Bendtsen.

The materials described as carrier for use with starch can also be usedwith the other barrier materials used according to the first aspect ofthe invention. However, generally a plastics film carrier or a plasticscoated thin paper carrier is preferred when using starch and the use ofa thin paper or a plastics coated thin paper carrier is preferred forbarrier materials such as PVOH which may be heated to temperatures wellabove 100° C. for drying and curing.

Starch for use in the invention may be of any conventional type althoughcertain starches provide better results than others under the conditionswe have used. Modified potato starch is preferred, such as Raisamyl 306(Raisio) which is hypochlorite oxidised. Other acceptable starchesinclude corn starch and derivatives, such as Cerestar 05773 ahydroxypropylated corn starch.

Starch derivatives that are suitable for use in the invention includeoxidised starch, cationic starch and hydroxpropylated starch.

It will be understood that when the gas barrier property of thepackaging laminates of the invention is referred to as being provided bya particular material, e.g. a composition of starch or a starchderivative and an inorganic laminar compound, this does not exclude thecase where the gas barrier property is the result of an interactionbetween the stated material and an adjacent layer in the laminate,rather than a bulk property of the stated material viewed in isolation.

It may be that a contributing mechanism in the improvement in barrierproperty noted when polyethylene is applied at a high temperature to alayer of starch comes from penetration of polyethylene molecules intothe starch, replacing water in starch crystals. Other polymers producinga similar effect may be used.

Said plastics layer may be applied to said composition of starch orstarch derivative and inorganic laminar compound by melt extrusion ormay be applied as a preformed film by hot pressure lamination e.g. witha heated roller. Generally, any technique may be employed in accordancewith this preferred embodiment that provides the required modificationof the barrier property of the starch.

Preferably said plastics layer is bonded to the layer of starch orstarch derivative and inorganic laminar compound at a temperature of atleast 200° C., preferably from 250 to 350° C. most preferably from 250to 330° C.

According to a second aspect of the invention, a laminated packagingmaterial is provided, which is produced according to the method of theinvention.

According to a third aspect of the invention, a packaging container isproduced by fold formation of a sheet or web-shaped laminated packagingmaterial obtained by the method according to the invention.

By applying, in a separate production stage, a liquid composition of apolymer dispersion or polymer solution and an inorganic laminar compoundas a barrier layer on at least one side of a carrier layer and dryingthe barrier layer during heating for driving off the liquid medium,preferably water, and thereafter combining and permanently uniting thecarrier layer with the applied, dried barrier layer to one side of thecore layer, there will be realised a laminate packaging material with abarrier layer possessing superior barrier properties.

Thanks to the fact that the barrier layer is not dried or cured atelevated temperature in connection with the lamination of the packagingmaterial, the risk of excessive water absorption into the core layer andof drying of the core layer of paper or paperboard—with consequentialrisk of crack formation in the core layer—is wholly eliminated.

Given that the plastics layer applied between the core layer and a papercarrier layer may include a substance serving as light barrier, ideallycarbon black, a light barrier layer will be realised whose unattractiveblack appearance may be concealed in a layer between the core layer anda thin paper layer carrying the barrier layer.

One important advantage of the method according to the aspect of thepresent invention is that the barrier layer produced in a separate stagemay be employed in the production of a laminated packaging material in acorresponding manner and using corresponding production equipment as areemployed today in the production of packaging materials with aluminumfoil as the oxygen gas barrier.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in greater detail hereinbelow, with the aid of non-restrictive examples of methods, as well aspackaging laminates—obtainable by the method, according to preferredembodiments of the present invention and with reference to theaccompanying drawings, in which:

FIG. 1 schematically illustrates a method of producing a carrier layerwith a barrier layer according to the present invention applied thereon;

FIG. 2 schematically illustrates a method of producing a laminatedpackaging material according to the present invention;

FIG. 3 is a cross sectional view through a laminated packaging materialaccording to the present invention;

FIG. 4 is a perspective view from above of a conventional,configurationally stable packaging container which is produced from alaminated packaging material according to the present invention;

FIG. 5 (a,b,c,d) schematically illustrate cross-sections of fourdifferent packaging laminates according to specific embodiments of theinvention; and

FIG. 6 (a,b,c,d) schematically illustrate the methods of manufacturingof the respective packaging laminates as described in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Drawings, FIGS. 1 and 2 schematically illustrate amethod according to the present invention chosen by way of example forproducing a laminated packaging material 10 shown in FIG. 3. A web of acarrier layer 11, for example of thin paper, which may preferably becoated with a thin layer of plastics, is unwound from a magazine reel 12and led past an applicator 13 (ideally a liquid film coating apparatus)disposed adjacent the web, by means of which at least one barrier layer14 of an aqueous composition comprising a dispersion or solution of apolymer and an inorganic laminar compound is applied on the one side ofthe carrier layer 11 in the form of a substantially cohesive barrierlayer 14. In the case of a plastics coated paper carrier layer, thepolymer dispersion or solution is preferably applied to the plasticscoated side. The quantity of applied solution may vary, but ispreferably in such an amount that a thoroughly integrated andsubstantially unbroken layer is formed after drying, for example approx.0.5-20 g/m², preferably 1-10 g/m², based on dry weight.

Where a composition of PVOH and inorganic laminar compound is used, thecarrier layer 11 preferably consists of a layer of thin paper with agrammage of approx. 5-35 g/m², preferably 7-25 g/m², more preferably10-20 g/m², but may also be a plastics film. However, thin paper enjoysthe advantage that it does not alter dimensions on temperature increasesin connection with drying and possible curing, which does not apply toplastic. Generally, where the polymer applied is to be cured at aboveabout 130° C., the use of plastics film as carrier layer is notrecommended.

The barrier layer 14 is applied on the carrier layer 11 in the form ofan aqueous composition, comprising a polymer dispersion or polymersolution and an inorganic laminar compound, the composition including apolymer with those properties which are desired to be added to thepackaging laminate in the form of a coated layer, for example a polymerwith functional hydroxyl groups, for instance polyvinyl alcohol,ethylene vinyl alcohol, starch, starch derivative, carboxy methylcellulose and other cellulose derivates or mixtures thereof.

The barrier layer 14 may also include a hydrophobic polymer as describedin WO97/22536, for example a styrene butadiene copolymer.

The barrier layer 14 may also include a polymer with functional groupswhich are reactive with the functional hydroxyl groups in theabovementioned polymer, for realising a cross-linked barrier layer 14.Such polymers may be polyolefins modified with carboxyl acid groups orgraft copolymers with monomers containing carboxyl acid groups in anolefin homo- or copolymer. Alternatively, such polymers may be randomselected copolymers of olefin monomers and monomers containingfunctional carboxylic acid groups, such as carboxylic acids, carboxylicacid anhydrides, metal salts of carboxylic acids or derivatives thereof.Specific examples of suitable functional polyolefins includepolyethylene and polypropylene homo- or copolymers grafted with maleicacid anhydride, ethylene acrylic acid (EAA) or ethylene rhetacrylic acid(EMAA), or random selected copolymers.

It is particularly preferred that the barrier layer 14 includes amixture of polyvinyl alcohol, ethylene acrylic acid copolymer and aninorganic laminar compound. The mixing ratio between polyvinyl alcoholand ethylene acrylic acid copolymer in the barrier layer 14 should besuch that the polyvinyl alcohol may form a blanket protection againstgas transport in the packaging laminate, at the same time as thequantity of ethylene acrylic acid copolymer should be sufficient to forma cohesive phase which partly protects the polyvinyl alcohol and partlyeffectively counteracts or prevents the transport of liquid through thepolymer of the barrier layer 14.

According to another preferred embodiment, the barrier layer 14 includesa mixture of starch and an inorganic laminar compound.

The web of carrier layer 11 is led, after coating, further past a dryingapparatus 15, e.g. an IR drier or a hot air drier which acts on thecoated side of the carrier layer 11 for driving off water and drying theapplied barrier layer 14 at web surface temperature of approx. 80-100°C.preferably approx. 90-95°C. and, where applicable, a curing temperaturefor cross-linking the functional groups included in the coated polymermixture, a web surface temperature of up to approx. 190°C. preferably170°C.

Finally, the finished carrier layer 11 with the applied barrier layer 14is rolled up and may subsequently be stored or employed direct in aconventional lamination process for the production of a laminatedpackaging material 10 possessing superior barrier properties.

The carrier layer 11 with the applied barrier layer 14 may ideally beemployed for the production of packaging material 10 in a correspondingmanner and using corresponding production equipment to that employed inthe production of packaging material with aluminum foil as the barrierlayer. FIG. 2 shows a web of a configurationally rigid but foldable corelayer with a grammage of approx. 100-500 g/m², preferably approx.200-300 g/m², which may be a conventional fiber layer of paper orpaperboard of suitable packaging qualities. The core layer 16 is ledthrough the nip between two rotating rollers 17 and is united with a webof carrier layer 11 with dried or cured barrier layer 14, during theapplication—employing an extruder 18—of one or more layers of extrudablethermoplastic 19, preferably polyethylene, between the core layer 16 andthe carrier layer 11. As shown, the barrier material 14 is preferablyfor the outer face of the carrier layer but it may alternatively be onthe inner face.

The thus laminated web is finally led through the nip between tworotating rollers 20 under the simultaneous application of thin layers21, 22 of extrudable thermoplastics, preferably polyethylene, againstboth outer sides of the web employing extruders 23, the finishedlaminated packaging material 10 according to the present inventionobtaining the cross-sectional structure schematically shown in FIG. 3.Alternatively, two extruders 23 may be disposed in sequence for theconsecutive extrusion of thin layers 21 and 22 of thermoplastic on therespective outer sides of the laminated web.

The two plastics layers 21 and 22 have for their purpose, on the onehand, to protect the packaging material 10 from the penetration ofmoisture and damp from the outside and, also the crucial function ofrendering the packaging material sealable by conventional so-calledthermosealing, whereby mutually facing layers of plastic may be joinedtogether under the supply of heat and pressure by surface fusion. Thethermosealing operation realises mechanically strong, liquid-tightsealing joints during the conversion of the packaging material intofinished packaging containers.

The outer plastics layer 22 which is applied on the packaging material10 on that side of the core layer 16 which, in the finished packagingcontainer, is intended to be turned to face towards the outside may beprovided with a suitable print of a decorative and/or informative naturefor identifying a packed product.

From the laminated packaging material according to the presentinvention, liquid-tight, dimensionally stable packages possessingsuperior oxygen gas barrier properties may be produced employing knownpackaging and filling machines which, in a continuous process form, filland seal the material into finished packages 50. An example of such aconventional, packaging container 50 is shown in FIG. 4.

By first uniting the longitudinal edges of a web-shaped laminatedpackaging material 10 into a tube which is filled with the contemplatedcontents, whereafter individual packages 50 are separated from the webby repeated transverse sealing of the tube below the level of thecontents. The packages 50 are separated from one another by incisions inthe transverse sealing zones and obtain the desired geometricconfiguration, normally parallelepipedic, by a final fold formation andsealing operation.

It should be noted that the various packaging laminates according to theinvention may comprise a multiple number of layers in addition to thoseshown in the drawings. It will thus be obvious to a person skilled inthe art that the number of layers may vary and that the description oilthe illustrated embodiments should not, therefore, be considered asrestrictive of the present invention.

FIG. 5a schematically illustrates a cross-section of a packaginglaminate according to a simple embodiment of the intention, carrying thegeneric reference numeral 10 a, while FIG. 6a schematically illustratesthe method (denoted 20 a) of manufacturing of the carrier layerstructure used in the laminate 10 a. The laminate 10 a comprises acarrier layer 11, whose surface has a smooth, essentially non-absorbingtexture. The carrier layer 11 may be a plastics film or a thin paperhaving said surface qualities. A thin paper substrate having a surfaceweight of about 5-35 g/m² is not able to absorb much from the liquidbarrier composition, both since it is very thin and since suchcommercially available thin papers usually have very smooth and glossy,hard surfaces. A particularly suitable paper for this purpose isso-called glassine paper, which, however, is rather expensive comparedto other commercially available papers. Suitably, the paper may be MGKraft paper (Munksjö) of from about 5 to about 35 g/m² surface weight,MG indicating that the paper is smooth on one surface, which is wherethe starch should be app: lied preferably. When the barrier compositionincludes starch or a starch derivative, the carrier layer 11 mostpreferably is a plastics film or a plastics coated thin paper carriersince it has the most advantageous surface properties.

A thin layer of an aqueous composition, comprising a solution ordispersion of starch and an inorganic laminar compound, is applied on tothe upper side of a web of substrate layer 11, which is led in thedirection of the arrow from a magazine reel (not shown) to a coatingstation 13 a. The aqueous composition is preferably applied by means ofliquid film coating technology, also called “dispersion coating” or “Wetcoating”, which is well known in the prior art of coating of aqueoussolutions and dispersions, but also other coating methods are feasibleaccording to the invention, depending on the viscosity of thecomposition. The aqueous composition including starch preferably isapplied in such a quantity that the applied and dried barrier layer 14has a thickness/surface weight of from about 0.5 to about 3 g/m².

The web coated with aqueous solution is led further to a drying station15 a at which the web is dried with aid of a drying apparatus forremoving water from the applied aqueous starch solution. Drying may becarried out by any conventional drying apparatus such as an infra-red(IR) drier or an air drier. Preferably, drying takes place at atemperature of about 80-100° C.

From the drying station the dried web, having an upper layer 14 ofstarch and inorganic laminar compound, is led further to an extruderstation at 23 a at which the web and barrier layer is further laminatedto a layer of plastics 21. The lamination of the starch surface to theplastics layer is carried out by means of surface fusion between theplastics layer and the layer including starch 14, which is obtained bysimultaneous application of heat and the plastics. Preferably, moltenpolymer is extruded on to the dried starch layer at the same time as theweb is led through the nip between two rotary cooling rollers 24 a, thusforming a finished packaging laminate providing the upper three layersof the packaging laminate 10 a as shown by a cross-section view in FIG.5a, having an outer layer of plastics 21, laminated to the starch layer14. The extruded plastics material is (preferably) a thermoplasticpolymer, preferably a polyethylene and most preferably LDPE, whichenables efficient conversion of the packaging laminate 10 a intoliquid-tight, dimensionally stable packages by heat sealing. Theextrusion temperature should be at least 200° C., preferably from about250° C. to about 330° C.

Alternatively, said surface fusion between the starch layer 14 and theplastic layer 21 may be obtained by laminating a pre-manufactured filmof thermoplastic to the dried starch layer 14 by means oil simultaneousapplication of heat and pressure, preferably by means of leading thestarch coated substrate and the plastic film together through a hotroller nip, whereby the temperature supplied by the hot rollers is atleast 200° C. and up to about 350° C., preferably from about 250° C. toabout 330° C.

The three layer laminates so produced may then be laminated to apaperboard core 16 as shown in FIG. 5a, by means of extrusion laminationwith an intermediate layer 19 of thermoplastic polymer, preferablypolyethylene, to produce the packaging laminate 10 a.

FIG. 5b schematically illustrates a cross-section of a packaginglaminate 10 b according to another embodiment of the invention and FIG.6b schematically illustrates the method (denoted 20 b) of manufacturingof the laminate 10 b.

According to this embodiment of the invention, the substrate or carrierlayer 11 is coated on both sides by an aqueous barrier composition inthe same way as described in the embodiment of FIGS. 5a and 6 a.

Consequently, the packaging laminate 10 b, which has been manufacturedby the method of FIG. 6b, comprises a carrier layer II as defined above,a thin layer of barrier composition (14, 14′) applied on to each side ofthe substrate layer 11 and the outer layers of plastics (21, 21′)laminated to the outer sides of respective barrier layer. In the case ofstarch in the barrier layer, the outer layers of plastics are applied bymeans of surface fusion with the starch barrier layer obtained bysimultaneous application of heat as described above. With such a layerstructure, a double gas barrier effect should be obtained.

Accordingly, with the method of FIG. 6b, a thin layer of an aqueousbarrier composition is applied on to each side of a web of a carrierlayer 11, which is led in the direction of the arrow from a magazinereel (not shown) to a coating station 13 b. An aqueous compositionincluding starch and an inorganic laminar compound is preferably appliedby means of dispersion coating technology in such a quantity on to eachside of the substrate layer 11, that the applied and dried starch layers14, 14′ each have a thickness/surface weight of from about 0.5 to about3 g/m².

An aqueous composition including PVOH and an inorganic laminar compoundis preferably applied in such a quantity that the applied and driedstarch layers 14, 14′ each have a thickness/surface weight of from about1 to about 10 g/m².

The web coated with aqueous solution is led further to a dying station15 b at which the web is dried with the aid of a drying apparatus forremoving water from the applied layers of aqueous starch solution.Preferably, drying takes place at a temperature of about 80-100° C., asdescribed above. Optionally, the dried barrier layer is then cured at ahigher temperature as described above.

From the drying station the dried web, having an upper barrier layer 14and a lower barrier layer 14′, is led further via a bending roller 25 toan extruder station at 23 b at which the web is further coated with alayer of plastics on each side. Thus the layers of plastics 21 and 21′are applied by means of respective extruders 26, 27 operating on eachside of the web. The molten polymer is extruded on to the dried barrierlayers at the same time as the web is led through the nip between tworotary cooling rollers 24 b, in principle as described above, thusforming a finished packaging laminate 10 b as shown by a cross-sectionview in FIG. 5b. The laminate 10 b is united with a core layer, andformed to a finished package as shown in FIG. 4.

FIG. 5c thus schematically illustrates a cross-section of a packaginglaminate 10 c according to an alternative embodiment of the inventionwhile FIG. 6c schematically illustrates the method (denoted 20 c) ofmanufacturing of the laminate 10 c.

A paper or paperboard core layer for use in the invention usually has athickness of from about 100 pm up to about 400 pm, and a surface weightof approximately 100-500 g/m², preferably about 200-300 g/m².

According to the method 20 c, a first web of the core layer 16, is ledin the direction of the arrow from a magazine reel (not shown) to anextrusion lamination station 28 at which a second web of the substratelayer 11 having a dried layer of barrier composition applied on to eachside 14, 14′ is superposed and laminated to the core layer by means ofan intermediate melt extruded lamination layer 19 of a thermoplasticspolymer, preferably a polyethylene and most preferably LDPE.

The web of laminated core, barrier and carrier layers 16′ is further ledto an extruder station 29 at which an outer layer of thermoplastics 21,22, such as preferably LDPE, is further extruded on to each side of thelaminate 16, such that the barrier layer on the outer side of thesubstrate layer 11. which is opposite to the side which is laminated tothe core layer, as well as the opposite side of the core layer 16, areboth coated by the extruded thermoplastics, thus forming layers 21 and22.

Suitable thermoplastics for the outer layer 14 are polyolefins,preferably polyethylenes and most preferably low density polyethylenessuch as, for example LDPE, linear LDPE (LLDPE) or single site catalystmetallocene polyethylenes (m-PE). The outer layer 22, which eventuallywill form the outside of the packaging container manufactured from thepackaging laminate, may alternatively be applied on to the core web 16in a step before the coating and drying steps of the barriercomposition.

FIG. 5d schematically illustrates a cross-section of a packaginglaminate 10 d according to another embodiment of the invention whileFIG. 6d schematically illustrates the method (denoted 20 d) ofmanufacturing of the laminate 10 d. The packaging laminate 10 d ismanufactured by applying and drying of a thin layer of an aqueousbarrier composition comprising a dispersion or solution of a polymer andan inorganic laminar compound 14 on to the upper side of a carrier layer11, which is constituted of a plastic E film, as described in the method20 a above, in an initial step.

According to the method 20 d, a first web of the core layer 16, is ledin the direction of the arrow from a magazine reel (not shown) to anextrusion lamination station 28′ at which a second web of the carrierlayer 11 having a dried layer of barrier composition applied on to oneside, is super-posed such that the barrier layer 14 is directed towardsthe core layer and laminated to the core layer by means of anintermediate melt extruded lamination layer of a thermoplastics polymer,preferably a polyethylene and most preferably LDPE. The carrier layer11, i.e. the plastics film, may form an outer layer of the packaginglaminate to be directed inwards in a packaging container manufacturedtherefrom, thus providing a container inside layer. In a final extruderstation 29′, the outer thermoplastic layer 17 is applied by means ofextrusion coating.

A problem of the laminates for example described in WO97/16312 is thattheir manufacture would require completely different machinery in thelamination and converting process to that of the paperboard laminatesusing aluminum foil as a gas barrier which are in conventional use. Suchpackaging laminates are made by extrusion laminating a paper boardsubstrate to the barrier foil using polyethylene. In contrast, as can beseen from the above, a carrier layer of plastics or thin paper bearing abarrier composition comprising a hydrogen-bonding polymer and aninorganic laminar compound coating on one or both faces, with or withoutplastics already applied to the starch layer or to one or both of them,can simply be substituted for the aluminum foil in conventionalmachinery with minor adjustment. The preparation of the gas barrierbearing carrier material can be done completely separately in anotherfacility if need be so that an existing converting line in a factory canreadily be adapted to use the new materials.

Thus a further important advantage by a preferred embodiment of themethod illustrated, is that the steps of application and drying of theliquid gas barrier composition may be performed off the laminationprocessing line, thus avoiding costly modifications and re-constructionof the lamination equipment in the manufacturing of packaging laminateshaving a core layer. By applying the barrier layer on to a thin carrierlayer such as a plastics film or a thin paper having a smooth,essentially non-absorbing surface, in the sub-sequence lamination withfurther layers of plastics and a core layer, the lamination operationmay be performed using the safe equipment and process as is used today,when laminating for example aluminum foil and inside layers.

From sheet or web-shaped, preferably pre-creased and colour decorated,blanks of the packaging laminate 10, liquid-tight, dimensionally stablepackages of the single-use disposable type are produced in accordancewith—conventional “form-fill-seal” technology, according to which thepackages are formed, filled and sealed by means of modern, rationalpackaging and filling machines. From, for example, a web of thepackaging laminate, such packages are produced in that the web is firstreformed into a tube, by both longitudinal edges of the tube beingunited with another by heat sealing in a longitudinal overlap jointseal. The tube is filled with the pertinent contents, for example liquidfood, and is divided into individual packages by repeated transversesealings of the tube, transversely across the longitudinal axis of thetube, beneath the level of the contents in the tube. The packages arefinally separated from one another by transverse incisions along thetransverse seals, thus forming pillow-shaped sealed packages. Thepillow-shaped packages may be distributed as such or first be given adesired geometric, normally parallelepipedic form by an additionalforming and heat-sealing operation in a per se known manner.

Using the methods and materials described above by applying an aqueousbarrier composition comprising a dispersion solution of starch or aderivative and an inorganic laminar compound on to a substrate layer forsupporting the barrier layer, which consists of a specifically chosenmaterial, in combination with subsequent drying and lamination to alayer of plastics by heat fusion of the plastics surface, highlyimproved oxygen gas barrier properties are obtained in packaginglaminates compared to those of WO97/16312. The improvement in the gasbarrier properties of the laminated barrier layer has been improvedradically into an excellent so called high performance barrier layer.The best gas barrier results have been obtained when the substrate layerconsists of a polymer or has a polymer coated surface, but also a thinpaper layer having a surface weight of approximately 7-35 g/m² withsmooth, essentially non-absorbing surfaces, will provide improved gasbarrier properties compared to those previously known in connection withcompositions including starch.

Optimal gas barrier properties in the case of a barrier compositioncomprising starch are obtained when using a carrier layer of plastics orhaving a surface of plastics are, which is believed to be at leastpartly the result of the quality of the surface, i.e. smoothness andliquid repellence. Whilst the mechanism of the effect obtained using afusion bonded interface between starch polymer and plastics layers isnot fully understood, the optimal gas barrier properties may also partlybe the result of there being such an interface formed on both sides ofthe starch-containing layer, since the carrier layer to which thestarch-containing composition is applied is a plastics layer and thesame kind of phenomenon may occur at this interface upon the applicationof heat to the starch-containing layers and plastics layers.

A starch-containing gas barrier layer according to the invention isadvantageously applied in an amount of from about 0.5 to 5 g/m², dryweight. At amounts lower than 0.5 g/m², the tolerances of the layerthickness as well as the gas barrier properties will become lessreliable. On the other hand, at amounts exceeding about 3 g/m², therisks that the starch-based barrier layer may become brittle andinflexible will increase. However, amounts applied of up to about 5g/m², dry weight, are possible and for some type of packages and useseven higher amounts might be acceptable. The gas barrier property of thestarch-composition layer generally improves with increasing thickness.The optimal and preferred applied amount of starch ranges from about 1.5to about 2 g/m².

PREPARATION EXAMPLE 1

An aqueous dispersion of from about 1-5 weight % exfoliated flake shapedmineral particles (natural, e.g. Montmorillonite, or synthetic, e.g.Laponite) having an aspect ratio of about 50-5000, is blended with anaqueous solution of about 5-30 weight % of PVOH (having a molecularweight of 16000-200000 g/mol and a saponification degree of 95-100%) at60-90° C. during 2-8 hours. The dispersion of exfoliated laminar mineralparticles may be stabilised by means of a stabiliser additive.Alternatively, the laminar mineral particles are exfoliated in thePVOH-solution at 60-90° C. during 2-8 hours. Aqueous ethylene acrylicacid copolymer dispersion is added to the aqueous mixture of PVOH andmineral particles. The resulting mixture is dispersion coated by fromabout 1 to about 10 g/m² based on dry coating weight onto a thin plasticcoated paper carrier layer. The wet coating is applied as asolution/dispersion in water and dried at a web surface temperature of100-150° C. followed by curing at 170-190° C.

PREPARATION EXAMPLE 2

In preparing the barrier material/carrier material element, starch wasprepared for use in coating from a dry powder state by mixing 10 wt % ofstarch with water at ambient temperature to form a slurry.

An aqueous dispersion of from about 1-5 weight % exfoliated flake shapedmineral particles (natural, e.g. Montmorillonite, or synthetic, e.g.Laponite) having an aspect ratio of about 50-5000, is blended with theaqueous solution/dispersion of starch at 60-90° C. during 2-8 hours. Thedispersion of exfoliated laminar mineral particles may be stabilised bymeans of a stabiliser additive. Alternatively, the laminar mineralparticles are exfoliated in the starch slurry at 60-90° C. during 2-8hours.

The resulting slurry of starch and mineral particles was heated withmixing to from 90 to 95° C. and kept at that temperature for 30 minutes.During heating the starch swelled.

If possible, e.g. with Raisamyl 306 (Raisio), the starch was cooled toambient before use in coating. However, where this would have caused thestarch to gel, e.g. with CERESTAR, the starch composition was coated hot(60′).

A wet weight of approximately ten times the desired dry coating weightwas applied to the carrier layer in web form by means of a liquid filmcoating/dispersion coating method.

For the starch-containing composition a first drying stage using IRheating to a web surface temperature of 80 to 100° C. was used to speedthe drying process followed by a hot air drying step in which the starchcoating was hot air dried at web speed of 1 m/min at a temperature of110° C. Generally, a web surface temperature of 80 to 110° C. issuitable depending on the linespeed.

Preferably, the dried starch layer was extrusion coated with LDPE. About25 g/m² of LDPE was extruded on to the dried starch, layer at about 200m/minute, 325° C., cooling roller at 10-15° C., as above. The distancebetween the extrusion die to the web was normally 10-30 cm. The extrudedLDPE hit the web just before entering between the cooling roller and thecounter pressure roller.

It will be obvious to a person skilled in the art that the presentinvention is not restricted to the illustrated embodiment, but thatvarious modifications and alterations thereof may be put into effectwithout departing from the scope of the inventive concept as this isdefined in the appended claims. For example, the packaging materialstructures illustrated are naturally, not restricted to the illustratednumber of layers, but this number may be both greater and smaller, andmay also be freely varied in response to the desired filed of use of thepackaging material.

What is claimed is:
 1. A method of producing a laminated packagingmaterial comprising a core layer of paper or paperboard and a barrierlayer applied on one side of the core layer, wherein a liquid barriercomposition including a dispersion or solution of a polymer and aninorganic laminar compound is applied as a barrier layer on at least oneside of a carrier layer consisting of paper, said at least one side ofthe carrier layer having a smoothness of up to about 175 Bendtsen, andsaid liquid barrier composition is dried during heating for driving offthe dispersant or solvent, whereafter the carrier layer with theapplied, dried barrier layer is combined and permanently united with oneside of the core layer.
 2. A method of producing a laminated packagingmaterial comprising a core layer of paper or paperboard and a barrierlayer applied on one side of the core layer, wherein a liquid barriercomposition including a dispersion or solution of a polymer and aninorganic laminar compound is applied as a barrier layer on at least oneside of a carrier layer consisting of paper, said at least one side ofthe carrier layer having a smoothness of up to about 150 Bendtsen, andsaid liquid barrier composition is dried during heating for driving offthe dispersant or solvent, whereafter the carrier layer with the applieddried barrier layer is combined and permanently united with one side ofthe core layer.
 3. A method as claimed in claim 2, wherein saidinorganic laminar compound is dispersed to an exfoliated and delaminatedstate in the liquid barter composition and in the dried barrier layer.4. A method as claimed in claim 2, wherein said barrier layer is appliedby means of liquid film coating with said liquid barrier compositionincluding said inorganic laminar compound.
 5. A method as claimed inclaim 2, wherein the barrier layer includes from about 1 to about 30weight % of the inorganic laminar compound, based on dry coating weight.6. A method as claimed in claim 2, wherein the barrier layer includesfrom about 70 to about 99 weight % of polymer, based on dry coatingweight.
 7. A method as claimed in claim 2, wherein the amount of theliquid barrier composition coated onto the carrier layer is from about 1to about 10 g/m² based on dry coating weight.
 8. A method as claimed inclaim 2, wherein the liquid barrier composition applied as said barrierlayer includes said polymer, and said polymer having functional hydroxylgroups.
 9. A method as claimed in claim 8, wherein said polymer withfunctional hydroxyl groups is polyvinyl alcohol, ethylene vinyl alcohol,starch, starch derivatives, carboxyl methyl cellulose and othercellulose derivatives, or a mixture of two or more thereof.
 10. A methodas claimed in claim 2, wherein said liquid gas barrier compositionapplied as said barrier layer is dried and optionally cured at atemperature of approx. 80-230° C.
 11. A method as claimed in claim 2,wherein said liquid gas barrier composition applied as said barrierlayer also includes a polymer with functional carboxylic acid groups.12. A method as claimed in claim 11, wherein said polymer withfunctional carboxylic acid groups is ethylene acrylic acid copolymer,ethylene methacrylic acid copolymer or a mixture thereof.
 13. A methodas claimed in claim 12 wherein said barrier layer consists essentiallyof a mixture of polyvinyl alcohol, ethylene acrylic acid copolymer andthe inorganic laminar compound.
 14. A method as claimed in claim 3,wherein the barrier layer consists essentially of a mixture of starch orstarch derivative and the inorganic laminar compound.
 15. A method asclaimed in claim 2, wherein the dried barrier layer is cured at atemperature of a surface of the carrier layer of up to 190° C.
 16. Amethod as claimed in claim 2, wherein the liquid barrier compositionapplied as a barrier layer is dried at a web surface temperature of 140to 160° C. and is cured at a web surface temperature of from 170 to 190°C.
 17. A method as claimed in claim 2, wherein said carrier layerconsists of paper with a grammage of approx. 5-35 g/m².
 18. A method asclaimed in claim 2, wherein said carrier layer consists of plasticcoated paper.
 19. A method as claimed in claim 2, wherein the carrierlayer bearing at least one barrier layer is combined and united with thecore layer by extrusion of a layer of thermoplastics therebetween.
 20. Amethod as claimed in claim 2, wherein the carrier layer bears saidbarrier layer on one side thereof and is combined with the core layer byextrusion of a layer of thermoplastics between the earner layer and thecore layer.
 21. A method as claimed in claim 20, wherein an outer layerof thermoplastics is applied on the barrier layer by means of extrusion.22. A method as claimed in claim 20, wherein the carrier layer bearssaid barrier layer on one or both sides and is combined with the corelayer by extrusion of a layer of thermoplastics between the core layerand a said barrier layer.
 23. A method as claimed in claim 22, whereinthe carrier layer bears said barrier layer on both sides thereof and alayer of thermoplastics is applied to the outer layer of barriermaterial by extrusion.
 24. A method as claimed in claim 19, wherein thelayer of thermoplastics applied between the core layer and the carrierlayer or said barrier layer includes a substance functioning as a lightbarrier.
 25. A method as claimed in claim 2, wherein said at least oneside of the carrier layer has a smoothness of up to about 100 Bendtsen.